6 research outputs found
Magnetically Guided Nano–Micro Shaping and Slicing of Silicon
Silicon is one of the most important materials for modern
electronics,
telecom, and photovoltaic (PV) solar cells. With the rapidly expanding
use of Si in the global economy, it would be highly desirable to reduce
the overall use of Si material, especially to make the PVs more affordable
and widely used as a renewable energy source. Here we report the first
successful direction-guided, nano/microshaping of silicon, the intended
direction of which is dictated by an applied magnetic field. Micrometer
thin, massively parallel silicon sheets, very tall Si microneedles,
zigzag bent Si nanowires, and tunnel drilling into Si substrates have
all been demonstrated. The technique, utilizing narrow array of Au/Fe/Au
trilayer etch lines, is particularly effective in producing only micrometer-thick
Si sheets by rapid and inexpensive means with only 5 μm level
slicing loss of Si material, thus practically eliminating the waste
(and also the use) of Si material compared to the ∼200 μm
kerf loss per slicing and ∼200 μm thick wafer in the
typical saw-cut Si solar cell preparation. We expect that such nano/microshaping
will enable a whole new family of novel Si geometries and exciting
applications, including flexible Si circuits and highly antireflective
zigzag nanowire coatings
3D Branched Nanowire Photoelectrochemical Electrodes for Efficient Solar Water Splitting
We report the systematic study of 3D ZnO/Si branched nanowire (b-NW) photoelectrodes and their application in solar water splitting. We focus our study on the correlation between the electrode design and structures (including Si NW doping, dimension of the trunk Si and branch ZnO NWs, and b-NW pitch size) and their photoelectrochemical (PEC) performances (efficiency and stability) under neutral conditions. Specifically, we show that for b-NW electrodes with lightly doped p-Si NW core, larger ZnO NW branches and longer Si NW cores give a higher <i>photocathodic</i> current, while for b-NWs with heavily doped p-Si NW trunks smaller ZnO NWs and shorter Si NWs provide a higher <i>photoanodic</i> current. Interestingly, the photocurrent turn-on potential decreases with longer p-Si NW trunks and larger ZnO NW branches resulting in a significant photocathodic turn-on potential shift of ∼600 mV for the optimized ZnO/p-Si b-NWs compared to that of the bare p-Si NWs. A photocathode energy conversion efficiency of greater than 2% at −1 V <i>versus</i> Pt counter electrode and in neutral solution is achieved for the optimized ZnO/p-Si b-NW electrodes. The PEC performances or incident photon-to-current efficiency are further improved using Si NW cores with smaller pitch size. The photoelectrode stability is dramatically improved by coating a thin TiO<sub>2</sub> protection layer using atomic-layer deposition method. These results provide very useful guidelines in designing photoelectrodes for selective solar water oxidation/reduction and overall spontaneous solar fuel generation using low cost earth-abundant materials for practical clean solar fuel production
Adsorption Behavior of Dyestuffs on Hollow Activated Carbon Fiber from Biomass
<div><p>This study focuses on the adsorption behavior of typical dyestuffs (methylene blue and reactive black 5) on hollow activated carbon fibers (ACFs) obtained from Kapok- and Hasuo-seed based biomass. It was found that the adsorption of dyestuffs on ACFs increased with increasing pH and temperature. In addition, the Hasuo-seed based ACFs showed higher adsorption capacities than the Kapok-seed based ACFs for dyestuffs. It was also determined from the adsorption energy distribution results that the ACFs are having energetically heterogeneous surfaces. The results clearly indicated that the prepared ACF in this study could efficiently remove dyes dissolved in water.</p></div
Solution-Processed CoFe<sub>2</sub>O<sub>4</sub> Nanoparticles on 3D Carbon Fiber Papers for Durable Oxygen Evolution Reaction
We report CoFe<sub>2</sub>O<sub>4</sub> nanoparticles (NPs) synthesized using a facile hydrothermal growth
and their attachment on 3D carbon fiber papers (CFPs) for efficient
and durable oxygen evolution reaction (OER). The CFPs covered with
CoFe<sub>2</sub>O<sub>4</sub> NPs show orders of magnitude higher
OER performance than bare CFP due to high activity of CoFe<sub>2</sub>O<sub>4</sub> NPs, leading to a small overpotential of 378 mV to
get a current density of 10 mA/cm<sup>2</sup>. Significantly, the
CoFe<sub>2</sub>O<sub>4</sub> NPs-on-CFP electrodes exhibit remarkably
long stability evaluated by continuous cycling (over 15 h) and operation
with a high current density at a fixed potential (over 40 h) without
any morphological change and with preservation of all materials within
the electrode. Furthermore, the CoFe<sub>2</sub>O<sub>4</sub> NPs-on-CFP
electrodes also exhibit hydrogen evolution reaction (HER) performance,
which is considerably higher than that of bare CFP, acting as a bifunctional
electrocatalyst. The achieved results show promising potential for
efficient, cost-effective, and durable hydrogen generation at large
scales using earth-abundant materials and cheap fabrication processes
Solution-Processed CoFe<sub>2</sub>O<sub>4</sub> Nanoparticles on 3D Carbon Fiber Papers for Durable Oxygen Evolution Reaction
We report CoFe<sub>2</sub>O<sub>4</sub> nanoparticles (NPs) synthesized using a facile hydrothermal growth
and their attachment on 3D carbon fiber papers (CFPs) for efficient
and durable oxygen evolution reaction (OER). The CFPs covered with
CoFe<sub>2</sub>O<sub>4</sub> NPs show orders of magnitude higher
OER performance than bare CFP due to high activity of CoFe<sub>2</sub>O<sub>4</sub> NPs, leading to a small overpotential of 378 mV to
get a current density of 10 mA/cm<sup>2</sup>. Significantly, the
CoFe<sub>2</sub>O<sub>4</sub> NPs-on-CFP electrodes exhibit remarkably
long stability evaluated by continuous cycling (over 15 h) and operation
with a high current density at a fixed potential (over 40 h) without
any morphological change and with preservation of all materials within
the electrode. Furthermore, the CoFe<sub>2</sub>O<sub>4</sub> NPs-on-CFP
electrodes also exhibit hydrogen evolution reaction (HER) performance,
which is considerably higher than that of bare CFP, acting as a bifunctional
electrocatalyst. The achieved results show promising potential for
efficient, cost-effective, and durable hydrogen generation at large
scales using earth-abundant materials and cheap fabrication processes
Tailoring n‑ZnO/p-Si Branched Nanowire Heterostructures for Selective Photoelectrochemical Water Oxidation or Reduction
We
report the fabrication of three-dimensional (3D) branched nanowire
(NW) heterostructures, consisting of periodically ordered vertical
Si NW trunks and ZnO NW branches, and their application for solar
water splitting. The branched NW photoelectrodes show orders of magnitudes
higher photocurrent compared to the bare Si NW electrodes. More interestingly,
selective photoelectrochemical cathodic or anodic behavior resulting
in either solar water oxidation or reduction was achieved by tuning
the doping concentration of the p-type Si NW core. Specifically, n-ZnO/p-Si
branched NW array electrodes with lightly doped core show broadband
absorption from UV to near IR region and photocathodic water reduction,
while n-ZnO/p<sup>+</sup>-Si branched NW arrays show photoanodic water
oxidation with photoresponse only to UV light. The photoelectrochemical
stability for over 24 h under constant light illumination and fixed
biasing potential was achieved by coating the branched NW array with
thin layers of TiO<sub>2</sub> and Pt. These studies not only reveal
the promise of 3D branched NW photoelectrodes for high efficiency
solar energy harvesting and conversion to clean chemical fuels, but
also developing understanding enabling rational design of high efficiency
robust photocathodes and photoanodes from low-cost and earth-abundant
materials allowing practical applications in clean renewable energy